Stretchable, tough, and self-healing elastomer and applications thereof

ABSTRACT

Various embodiments are directed to apparatuses and methods involving an elastomer material comprising a flexible polymer backbone with a particular ratio of at least first moieties and second moieties. The first moieties provide a first number of dynamic bonds resulting from interactions between the first moieties and the second moieties provide a second number of dynamic bonds resulting from interactions between the second moieties, the second number of dynamic bonds having a weaker bonding strength than the first number of dynamic bonds. The elastomer material, based on the ratio of the first moieties and second moieties, exhibits autonomous self-healing, a particular toughness, and is stretchable.

SUMMARY

Aspects of various embodiments are directed to a stretchable, tough, andself-healing elastomer and applications thereof, including applicationsof wearable electronics.

In the following discussion, various implementations and applicationsare disclosed to provide an understanding of the instant disclosure byway of non-limiting example embodiments.

In certain example embodiments, aspects of the present disclosure aredirected to various elastomer materials and polymer films formed usingthe elastomer material. The elastomer material can comprise and/orinvolve a flexible polymer backbone; exemplary polymers (non-limitingmaterials) in this regard include polydimethylsiloxane (PDMS),polyethyleneoxide (PEO), Perfluoropolyether (PFPE), polybutylene (PB),poly(ethylene-co-1-butylene), poly(butadiene), hydrogenatedpoly(butadiene), poly(ethylene oxide)-poly(propylene oxide) blockcopolymer or random copolymer, and poly(hydroxyalkanoate), with aparticular ratio of at least a first type of moieties that provide afirst number of dynamic bonds resulting from interactions between thefirst type of moieties (e.g., hydrogen or other bonding sites withrelatively strong bonds) and a second type of moieties that provide asecond number of dynamic bonds resulting from interactions between thesecond type of moieties (e.g., hydrogen or other bonding sites of aweaker bonding strength than the first number of hydrogen or otherbinding sides or with relatively weak bonds) in polymer chains, andfilms formed therefrom. As may be appreciated, dynamic bonds include orrefer to bonds that can be reformed, once broken due to mechanicalforces, at room temperature or elevated temperature, such as hydrogenbonds, metal-ligand bonds, guest-host interactions, and/orsupramolecular interactions. Such films exhibit self-healing, are tough,and are stretchable, consistent with one more embodiments and/or one ormore mechanisms described herein. In specific aspects, the polymer filmcan include a polydimethylsiloxane (PDMS) polymer backbone with aparticular ratio of 4,4′-methylenebis(phenyl urea) (MPU) and isophoronebisurea (IU). In such aspects, the first moieties include4,4′-methylenebis(phenyl urea) (MPU) and the second moieties includeisophorone bisurea (IU), although embodiments are not so limited. The atleast first moieties and second moieties can be spaced randomly orequally from another. For example, the polymer segment between themoieties can typically be between 1,000 Dalton to 25,000 Dalton,although embodiments in accordance with the present disclosure are notso limited.

More specific example embodiments are directed to methods/apparatusescomprising and/or involving use of the elastomer material to form apolymer film. The film is colorless and transparent, and exhibitsautonomous self-healing and stretching of up to 1,200 percent strainwithout rupturing. In some specific aspects, the film can be stretchedup to 3,000 percent and exhibits a Young's modulus of between 0.22 and1.5 megapascal (MPa). In other specific and related aspects, the polymerfilm exhibits notch-insensitive stretching and a fracture energy ofaround 12,000 Joule per meter squared (J/m²).

In more specific aspects, the mechanical properties of the elastomermaterial (e.g., PDMS-MPUx-IU1-x) is due to the different crosslinkstrength of the first and second moieties (or more moieties, in variousembodiments), such as the different crosslink strength of MPU and IU.The polymer film can provide or otherwise include dynamic bondingresulting from interactions between the first moieties and interactionsbetween the second moieties. More specifically, the first moietiesprovide a first number of dynamic bonds due to interactions betweenfirst moieties and the second moieties provide a second number ofdynamic bonds due to interaction between the second moieties. Inspecific aspects, the polymer film can include a first number of dynamicbonds resulting from MPU-MPU interactions and a second number of dynamicbonds resulting from IU-IU interactions. The IU-IU inter-bonding caninclude bonding of a lower strength than the MPU-MPU inter-bonding. Thepolymer film can include different ratios of MPU and IU units, such aspolymer films which include a ratio of MPU units to IU units of 0.4 to0.6, 0.3 to 0.7 and/or 0.2 to 0.8. Furthermore, the polymer film canexhibit notch-insensitive stretching and a fracture energy of around15,000 J/m².

The ratio of MPU and/or IU units in the polymer film can be adjusted tooptimize mechanical properties of the film. For example, the ratio ofMPU can be decreased to increase the fracture strain of the polymerfilm, and to decrease the Young's modulus and fracture energy. In otheraspects, the ratio of MPU is increased to increase the Young's modulusand fracture energy. Further, polymer films formed ofPDMS-MPU_(0.2)-IU_(0.8) and PDMS-MPU_(0.3)-IU_(0.7) can exhibit fasterhealing and higher self-healing efficiencies given the same healing timeas a polymer film formed of PDMS-MPU_(0.4)-IU_(0.6.)

In related and more specific aspects, the polymer film exhibitsautonomous self-healing in the presents of water, sweat, and/orartificial sweat, among other types of liquids. For example, the polymerfilm can be severed and the severed polymer film is healed in water for24 hours. The resulting healed film can be stretched up to 1,100 percentstrain without rupturing.

A number of related aspects are directed to an elastomer materialcomprising a flexible polymer backbone with a particular ratio of atleast first moieties and second moieties. The first moieties provide afirst number of dynamic bonds resulting from interactions between thefirst moieties. The second moieties provide a second number of dynamicbonds resulting from interactions between the second moieties, where thesecond number of dynamic bonds have a weaker bonding strength than thefirst number of dynamic bonds. In specific aspects, the first moietiesform up to four hydrogen bonds with another of the first moieties andthe second moieties form less than four (e.g., such as, up to two)hydrogen bonds with another of the second moieties. The elastomermaterial, based on the ratio of the at least first moieties and secondmoieties, exhibits autonomous self-healing, a particular toughness, andparticular stretchability. For example, the elastomer material exhibitsa Young's modulus of between 0.1 and 3.0 MPa and stretching of between1,200 and 3,000 percent without rupturing. In other examples, theelastomer material can stretch up to 3,000 percent and exhibits aYoung's modulus of between 0.22 and 1.5 MPa.

As previously described, the flexible polymer backbone is selected fromthe group consisting of: PDMS, PEO, PFPE, PB,poly(ethylene-co-1-butylene), poly(butadiene), hydrogenatedpoly(butadiene), polybutylene, poly(ethylene oxide)-poly(propyleneoxide) block copolymer or random copolymer, and poly(hydroxyalkanoate).The first moieties can include MPU and the second moieties can includeIU. In some related and more-specific aspects, the particular ratio ofMPU moieties to IU moieties is selected from the group consisting of:0.4 to 0.6, 0.3 to 0.7 and 0.2 to 0.8. Additionally, the elastomermaterial can include a supramolecular network formed as a polymer filmconfigured and arranged to exhibit the autonomous self-healing andnotch-insensitive stretching of 1,200-1,500 percent by self-recoverableenergy dissipation in the film.

Related and more specific aspects are directed to a polymer film thatincludes a supramolecular network of elastomer material. Similarly tothat described above, the elastomer material has a flexible polymerbackbone with a particular ratio of at least first moieties and secondmoieties. The first moieties provide a first number of dynamic bondsresulting from interactions between the first moieties and the secondmoieties provide a second number of dynamic bonds resulting frominteractions between the second moieties, the second number of dynamicbonds having a weaker bonding strength than the first number of dynamicbonds. The polymer film exhibits autonomous self-healing, a Young'smodulus of between 0.1 and 3.0 MPa, and stretching of between 1,200 and3,000 percent without rupturing. In related and more specific aspects,the polymer film is colorless and transparent, and the first moietiesinclude MPU and the second moieties include IU, and the flexible polymerbackbone is selected from the group consisting of: PDMS, PEO, PFPE, PB,poly(ethylene-co-1-butylene), poly(butadiene), hydrogenatedpoly(butadiene), polybutylene, poly(ethylene oxide)-poly(propyleneoxide) block copolymer or random copolymer, and poly(hydroxyalkanoate).

The polymer film exhibits mechanical properties including theself-healing, the Young's modulus and the stretching due to differentcrosslink strength of the first and second numbers of dynamic bonds. Ina number of specific aspects, polymer film is configured and arranged tobe stretched up to 3,000 percent and exhibits a Young's modulus ofbetween 0.22 and 1.5 and/or exhibits notch-insensitive stretching and afracture energy of around 15,000 J/m². The polymer film can exhibit theautonomous self-healing in the presence of liquid (water, sweat, and/orin the presents of artificial sweat).

Other aspects are directed to methods of forming the elastomermaterial/polymer film. The elastomer material can be formed bydissolving PDMS-MPUx-IU1-x in CHCl₃ and stirring while heating to form aviscous solution and cooling the viscous solution to room temperature.The viscous solution is then poured into a substrate and dried to form apolymer film, which can be removed from the substrate. The polymer filmcan be further processed, such as solution processing or molding andbonding at elevated temperatures or room temperature.

Another related method can include selecting a ratio of at least a firstmoiety and a second moiety based on one or more designated mechanicalproperties, forming a viscous solution that includes a flexible polymerand the ratio of the at least first moiety and the second moiety andfrom the viscous solution, forming a polymer film includes asupramolecular network of elastomer material. The elastomer materialhaving a flexible polymer backbone that includes the flexible polymerwith a particular ratio of first moieties and second moieties. The firstmoieties providing a first number of dynamic bonds resulting frominteractions between the first moieties and the second moietiesproviding a second number of dynamic bonds resulting from interactionsbetween the second moieties, the second number of dynamic bonds having aweaker bonding strength than the first number of dynamic bonds. Theformed polymer film exhibits autonomous self-healing, a Young's modulusof between 0.1 and 3.0 MPa, and stretching of between 1,200 and 3,000percent without rupturing. As previously described, selecting the ratioof first moieties and second moieties in the polymer film setsmechanical properties of the polymer film. For example, a decrease inthe first moiety increases a fracture strain and decreases the Young'smodulus and fracture energy. An increase in the first moiety increasesthe Young's modulus and fracture energy of the polymer film. In a numberof related aspects, the method further includes healing the severedpolymer film in water (for 24 hours), wherein the healed polymer film isconfigured and arranged to stretch up to 1,100 percent withoutrupturing.

In related specific aspects, the polymer film is used to form bulkfilms, three-dimensional self-healable objects, wearable electronics,robotic applications, self-healable electrode, self-healable capacitivestrain sensor, an array of strain sensors.

Various specific aspects are directed to using elastomer material,disclosed herein, in the application of a wearable circuitry. As withthe remarkable network of sensitive diverse sensors provided by humanskin, specific aspects of the present disclosure are applicable fortactile sensing, health monitoring, and temperature sensing. Consistentwith various embodiments, wearable circuitry including electronicsensors (e.g., force and otherwise) are formed using the elastomer ofthe present disclosure and are able to convert mechanical stimuli intosignals, which are then interpreted as beneficial to the particularapplication. As with human skin, particular embodiments includeelectronic skin (e-skin) devices which mimic properties of human skinfor applications such as wearable devices, artificial prosthetics,health monitoring and smart robots. In this context, e-skin is anartificial skin that mimics properties of skin using surface-interfacingstructures which are integrated with electronics (e.g., electroniccircuitry).

The above discussion/summary is not intended to describe each embodimentor every implementation of the present disclosure. The figures anddetailed description that follow also exemplify various embodiments.

BRIEF DESCRIPTION OF FIGURES

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

Various example embodiments may be more completely understood inconsideration of the following detailed description in connection withthe accompanying drawings, in which:

FIG. 1A shows an example of an elastomer material, in accordance withvarious embodiments;

FIG. 1B shows an example of an elastomer material and the supramolecularnetwork formed as a polymer film from the elastomer material, inaccordance with various embodiments;

FIG. 1C illustrates examples of different chemical structures ofpolymers synthesized and characterized herein, in accordance withvarious embodiments;

FIG. 1D illustrates a simulated dimer model of MPU-MPU and IU-IU, inaccordance with various embodiments;

FIGS. 2A-2H illustrate example properties of films formed using theelastomer material, in accordance with various embodiments;

FIGS. 3A-3N illustrate example properties of polymer films formed usingthe elastomer material, in accordance with various embodiments;

FIGS. 4A-4O illustrate example properties of films formed using theelastomer material, in accordance with various embodiments;

FIGS. 5A-5B illustrate transmittance of an example polymer film, inaccordance with various embodiments;

FIG. 6 illustrates an experimental result of testing the notchsensitivity and stretchability of an example polymer film, in accordancewith various embodiments;

FIGS. 7A-7B illustrate example stress curves of an example polymer film,in accordance with various embodiments;

FIGS. 8A-8B illustrate example stress applied to a notched polymer filmand unnotched polymer film, in accordance with various embodiments;

FIGS. 9A-9B illustrate example viscosity of polymer films, in accordancewith various embodiments;

FIGS. 10A-10E illustrate example spectrometry results of various polymerfilms, in accordance with various embodiments;

FIG. 11 illustrates an example differential scanning calorimetry thermalanalysis of PDMS-MPU_(0.4)-IU_(0.6), PDMS-MPU_(0.3)-IU_(0.7) andPDMS-MPU_(0.2)-IU_(0.8), in accordance with various embodiments;

FIGS. 12A-12E illustrate an example of self-healing of a polymer film inthe presence of water, in accordance with various embodiments;

FIGS. 13A-13B illustrate an example dynamic mechanical analysis ofPDMS-MPU_(0.4)-IU_(0.6) polymer film, in accordance with variousembodiments;

FIGS. 14A-14F illustrate various properties of example polymer films, inaccordance with various embodiments;

FIGS. 15A-15B illustrate an example of patterning the polymer film usinga mold, in accordance with various embodiments;

FIG. 16 illustrates an example stress cure of PDMS-MPU_(0.4)-IU_(0.6)film and self-healing electrode, in accordance with various embodiments;

FIG. 17A-17B illustrate liquid metal exhibited good wetting onPDMS-MPU_(0.4)-IU_(0.6) and FIG. 17B illustrates that the liquid metalcannot be bladed uniformly onto conventional PDMS film because of badwetting, in accordance with various embodiments;

FIGS. 18A-18D illustrate an example experiment of connecting aself-healing electrode to an LED lamp, in accordance with variousembodiments;

FIGS. 19A-19C illustrate example equipment that can be used to stretchthe polymer film and test the resulting strain, in accordance withvarious embodiments;

FIG. 20 illustrates an example capacitance change at differentfrequencies and over multiple cycles of stretching the polymer film, inaccordance with various embodiments;

FIGS. 21A-21B illustrate example of strain-sensors, in accordance withvarious embodiments; and

FIGS. 22A-22C illustrate example equipment that can be used to stretchthe polymer film with a notch and test the resulting strain, inaccordance with various embodiments.

While various embodiments discussed herein are amenable to modificationsand alternative forms, aspects thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit the disclosureto the particular embodiments described. On the contrary, the intentionis to cover all modifications, equivalents, and alternatives fallingwithin the scope of the disclosure including aspects defined in theclaims. In addition, the term “example” as used throughout thisapplication is only by way of illustration, and not limitation.

DETAILED DESCRIPTION

Aspects of the present disclosure are believed to be applicable tovariety of different elastomers that are tough, stretchable, andself-healing including elastomers that can self-heal in the presence ofliquid, and methods involving use of such elastomers to form electroniccircuitry. In certain implementations, aspects of the present disclosurehave been shown to be beneficial when used in the context of wearablecircuits, such as skin-like tactile sensor, but it will be appreciatedthat the instant disclosure is not necessarily so limited. Variousaspects may be appreciated through the following discussion ofnon-limiting examples which use exemplary contexts.

Accordingly, in the following description various specific details areset forth to describe specific examples presented herein. It should beapparent to one skilled in the art, however, that one or more otherexamples and/or variations of these examples may be practiced withoutall the specific details given below. In other instances, well knownfeatures have not been described in detail so as not to obscure thedescription of the examples herein. For ease of illustration, the samereference numerals may be used in different diagrams to refer to thesame elements or additional instances of the same element. Also,although aspects and features may in some cases be described inindividual figures, it will be appreciated that features from one figureor embodiment can be combined with features of another figure orembodiment even though the combination is not explicitly shown orexplicitly described as a combination.

Particular example embodiments are directed to a stretchable,self-healing, and mechanically tough elastomer, which can be used in avariety of electronic applications. In specific embodiments, theelastomer can include a self-healing silicon material with a fractureenergy of around 12,000 Joule per meter squared (J/m²) and that iscrosslinked (e.g., covalently or non-covalently) through multiplestrength dynamic bonding interactions. The elastomer can include asupramolecular network formed in film and that realizes autonomousself-healing and notch-insensitive stretching up to 1,200 or even up to3,000 percent due to self-recoverable energy dissipation. The elastomermaterial can be used for the fabrication of various stretchableelectronics. In addition, exceptional toughness of self-healing materialallows for facile implantation of electronic components on soft surfacesby suturing. Electronic circuits formed using the elastomer, such aswearable circuitry, can be malleable, intuitively programmable, andadaptive to the rapidly changing social and mechanical norms due to thestretchability and toughness of the elastomer.

In accordance with various embodiments, the elastomer material isself-healing. Surprisingly, the self-healing of the elastomer can takeplace in water in accordance with various specific embodiments. Theself-healing of the elastomer can be achieved by tuning the ratio ofstrong and weak crosslinking dynamic bonds in the supramolecularstructure that exhibits superior mechanical properties instretchability, toughness and self-healability (as further illustratedherein by FIGS. 2A-2H). As further explained herein, the differentstrong and weak crosslinking dynamic bonds are due to interactionsbetween different moieties. Various embodiments include differentelastomers formed of polydimethylsiloxane (PDMS) polymers with variousratios of 4,4′-methylenebis(phenyl urea) (MPU) and isophorone bisureaunits (IU) (as further illustrated by FIGS. 1A-1C). PDMS and dynamicbonds are chosen based on their biocompatible and containment of notoxic elements, therefore, making the resulting elastomer material anideal carrier for wearable electronics and biomedical applications. Inspecific embodiments, each of the PDMS-MPUx-IU1-x polymers formcolorless and transparent films (see, e.g., FIGS. 5A-5B). The films canbe stretched to sixteen times their original length at a loading rate of20 mm/min (200 percent/min) without rupturing (e.g., see, FIGS. 3A-3D).The polymer films, surprisingly, can achieve notch-insensitivestretching up to 1,200 percent strain, demonstrating an exceptionaltoughness (see, e.g., FIGS. 3E-3F and FIGS. 6A-6C). Other previouslyformed and typical PDMS substrates rupture at less than 200 percentstrain. Further, other commonly used substrates, such as polyurethaneand styrene-ethylene-butylene styrene (SEBS) rupture at 700 percent and280 percent strain, respectively. Moreover, the above-describedelastomer material, formed as a film, can achieve notch-insensitivestretching at more than 150 percent strain, indicating higher toughnessthan other material and fracture intolerance to tear (see, e.g., Table1). Notch-insensitive stretching, as used herein, includes or refers tostretching of a polymer film having a notch therein. Althoughembodiments are not so limited and can include a different types ofpolymer backbones and types and/or numbers of different moieties, asfurther described herein.

Turning now to the figures, FIG. 1A shows an example of an elastomermaterial, consistent with embodiments of the present disclosure. Theelastomer material 101 has a flexible polymer backbone 100 with aparticular ratio of first moieties 102 and second moieties 104. Based onthe particular ratio of first and second moieties 102, 104, theelastomer material 101 exhibits autonomous self-healing, a particulartoughness, and is stretchable. For example, the elastomer material canexhibit a Young's modulus of between 0.1 and 3.0 megapascal (MPa),stretching of between 1,200 and 3,000 percent without rupturing and/orfracture energy of between 12,000 to 15,000 Joule per meter squared(J/m²). Additionally, the elastomer material can self-heal, and afterhealing, can exhibit notch-insensitive stretching of between 1,200 to1,500 percent.

As illustrated, the elastomer material 101 includes a flexible polymerbackbone with a low glass transition temperature (Tg). As used herein,low Tg can include Tg values that are less zero degrees Celsius (C). Thepolymers include a particular ratio of at least first moieties (e.g.,strong dynamic bonding moiety) and second moieties (e.g., weak dynamicbonding moiety) having a lesser crosslink strength than the firstmoieties. The flexible polymer backbone 100 can includepolydimethylsiloxane (PDMS) polyethyleneoxide (PEO), Perfluoropolyether(PFPE), polybutylene (PB), poly(ethylene-co-1-butylene),poly(butadiene), hydrogenated poly(butadiene), polybutylene,poly(ethylene oxide)-poly(propylene oxide) block copolymer or randomcopolymer, or poly(hydroxyalkanoate).

The first moieties 102 and second moieties 104 can covalently bond toother first and second moiety units. For example, the first moieties 102provide a first number of dynamic bonds resulting from interactionsbetween the first moieties 102 and the second moieties 104 provide asecond number of dynamic bonds resulting from interactions between thesecond moieties 104. Dynamic bonds and/or bonding, as used herein,include or refer to bonds (e.g., bonding) that can be reformed, oncebroken due to mechanical forces, at room temperature or elevatedtemperature. Examples of dynamic bonding include hydrogen bonding,metal-ligand bonding, guest-host interactions, and supramolecularinteractions. As a specific example, the first moieties can formaggregation or crystallites that are nanometers or larger. The secondnumber of dynamic bonds, as further illustrated herein, have a weakerbonding strength than the first number of dynamic bonds. That is, thesecond moieties have a weaker crosslink strength than the first moieties(e.g., easier to break). As an example, the first moieties 102 form upto four dynamic (e.g., hydrogen) bonds with another of the firstmoieties and the second moieties 104 form less than four dynamic bonds(e.g., up to two hydrogen bonds) with another of the second moieties.The at least first moieties and second moieties can be spaced randomlyor equally from another within the polymer backbone. For example, thepolymer segment between the moieties can typically be between 1,000Dalton to 25,000 Dalton, although embodiments are not so limited.

In specific embodiments, the first moieties 102 include4,4′-methylenebis(phenyl urea) (MPU) and the second moieties 104 includeisophorone bisurea (IU). Different ratios of the first moieties 102 andsecond moieties 104 can provide different features exhibited by theresulting elastomer material 101. For example, the ratio can be selectedbased on one or more designated (e.g., desired or intended) mechanicalproperties of a resulting elastomer material and/or film formedtherefrom. In some embodiments, the particular ratio of MPU moieties toIU moieties is selected from the group consisting of: 0.4 to 0.6, 0.3 to0.7 and 0.2 to 0.8. The ratio can be adjusted to set mechanicalproperties such as fracture strain, fracture energy, and Young'smodulus. As specific examples, the elastomer material 101 can stretch upto 3,000 percent and exhibits a Young's modulus of between 0.22 and 1.5MPa and/or exhibits autonomous self-healing and notch-insensitivestretching of 1,200-1,500 percent by self-recoverable energydissipation.

In a number of embodiments, as further illustrated by FIG. 1B, theelastomer material 101 can include or be used to form a polymer film.The polymer film includes a supramolecular network of the elastomermaterial 101, as described above and including the various moieties andflexible polymer backbones. The polymer film can be colorless andtransparent, although embodiments are not so limited. The polymer filmcan exhibits autonomous self-healing, a Young's modulus of between 0.1and 3.0 MPa, and stretching of between 1,200 and 3,000 percent withoutrupturing. In specific embodiments, the polymer film exhibits theautonomous self-healing and notch-insensitive stretching of 1,200-1,500percent by self-recoverable energy dissipation in the film. In otherspecific embodiments, the polymer film can be stretched up to 3,000percent and exhibits a Young's modulus of between 0.22 and 1.5 MPa,exhibits notch-insensitive stretching and/or a fracture energy of around15,000 J/m2.

As previously described, the polymer film exhibits mechanical propertiesincluding the self-healing, the Young's modulus and the stretching dueto different crosslink strength of the first and second numbers ofdynamic bonds. In various embodiments, polymer film exhibit theautonomous self-healing in the presence of liquid, such as water, sweat,and/or in the presents of artificial sweat. As further illustrated anddescribed herein, the elastomer material 101 and/or polymer film can beused to forms three-dimensional self-healable objects, wearableelectronics, robotic applications, self-healable electrode,self-healable capacitive strain sensor, and/or an array of strainsensors.

FIG. 1B shows an example of an elastomer material and the supramolecularnetwork formed as a polymer film from the elastomer material, consistentwith embodiments of the present disclosure. As previously described, theelastomer material can include a supramolecular network formed as apolymer film 106 and that realizes autonomous self-healing, stretching,and is tough. The elastomer material includes, in specific embodiments,a PDMS 100-1, 100-2 with a particular ratio of at least first and secondmoieties, such as the illustrated MPU and IU units 103, 105. In specificembodiments, the ratio of MPU and IU units 103, 105 can be adjusted, asfurther illustrated herein. Although embodiments are not so limited andcan include a variety of different flexible polymer backbones, anddifferent units that provide the different crosslink strengths, asfurther illustrated herein. As may be appreciated, the term “unit” issometimes herein interchangeably used to refer to a moiety.Additionally, and in accordance with various embodiments, the flexiblepolymer backbone can include more than two different types of moieties,such as first, second, and third moieties.

More specifically, FIG. 1B illustrates the chemical structure ofPDMS-MPUx-IU1-x and the supramolecular structure therein. It is believedthat the mechanical properties of the elastomer material (e.g.,PDMS-MPUx-IU1-x) is due to the different crosslink strength of themoieties MPU and IU 103, 105. The MPU and IU units can provide differentstrength dynamic bonding. A first type of dynamic bonding can includecovalent bonds to hydrogens resulting from MPU-MPU interactions and asecond type of dynamic bonding can include a bond of lower strength thanthe first type of dynamic bonding that results from IU-IU interactions.For example, the MPU units (e.g., MPU 103) within the supramolecularstructure provide a first number of hydrogen bonds resulting fromrespective interactions between the MPU units (e.g., four hydrogen bondsbetween two MPU units). The IU units (e.g., IU 105) within thesupramolecular structure provide a second number of hydrogen bondsresulting from respective interactions between the IU units (e.g., twohydrogen bonds between two IU units).

A particular embodiment of elastomer includes a PDMS-MPU_(0.4)-IU_(0.6)film which includes ratio of MPU units to IU units of 0.4 to 0.6. Inexperimental embodiments, the PDMS-MPU_(0.4)-IU_(0.6) film can dissipatestrain energy efficiently, as shown by the observed pronouncedhysteresis in the loading and unloading curves (see, e.g., FIGS. 7A-7B).If the polymer film is first allowed to rest for 30 minutes andstretched again, the stress-strain curves can recover completely (see,e.g., FIGS. 7A-7B). Surprisingly, the PDMS-MPU_(0.4)-IU_(0.6) filmexhibits notch-insensitive stretching and a high fracture energy (around12,000 J/m2) among reported intrinsically tough materials as well asself-healing polymers (see, e.g., FIGS. 3E-G, 3N and FIGS. 8A-8B).

The mechanical properties of PDMS-MPU-IU can depend on the ratio of MPUand IU units. In various experimental embodiments, when the ratio of MPUunits in the polymer is decreased, the fracture strain of the polymerfilm is increased, and the Young's modulus and fracture energy aredecreased (see, e.g., FIGS. 3C, 3D, 3G and Table 1). For high mechanicalstrength, a higher MPU-MPU crosslinking density is used. It is believedthat the formation of the supramolecular structure in the polymer filmis driven by the combination of stronger MPU-MPU bonds, and the weakerMPU-IU or IU-IU bonds, as illustrated by FIG. 1B.

In other specific experimental embodiments, in CHCl₃ solution, the MPUunits are observed to interact primarily with the MPU unit rather thanthe IU unit, which can be confirmed by both concentration dependentviscosity measurements and nuclear magnetic resonance (NMR) measurements(see, e.g., FIGS. 9A-10E). Such a pre-crosslinked polymer network byMPU-MPU interactions in CHCl₃ solution gives rise to a supramolecularstructure in polymer film with both strong bonds and weak bonds uponremoval of the solvent. The resulting supramolecular structure isstretchable and has a high fracture energy (see, e.g., FIG. 2A). When anotched sample is stretched, the strong bonds are believed to besufficient to block the induced crack propagation while the weak bondssimultaneously break and dissipate strain energy. It is believed thatthe breakage of the weak bonds is able to reduce the stressconcentration on the strong bonds in the notch (see, e.g., FIG. 2C).Moreover, since the MPU and IU units are covalently linked by flexiblePDMS, the above process can synergistically take place (see, e.g., FIG.3G).

Accordingly, the illustrated elastomer material 103, 100-1, 105, 100-2can be used to form a polymer film 106 that is self-healing, tough, andstretchable. The polymer film is capable of autonomous self-healing evenwhen immersed in water. As a specific example and further illustratedherein, it is observed that the scar on a cut polymer film 106(PDMS-MPU_(0.4)-IU_(0.6)) can almost disappear after healing at roomtemperature for three days (see, e.g., FIGS. 3I-3J). The healed polymerfilm 106 is again able to be stretched to 1,500 percent after 48 hourswith self-healing efficiency of 78 percent (see, e.g., FIG. 3H and Table1). Polymers with lower MPU ratios, such as PDMS-MPU_(0.2)-IU_(0.8) andPDMS-MPU_(0.3)-IU_(0.7), show faster healing and higher self-healingefficiencies given the same healing time (see, e.g., Table 1). Thisobserved ambient self-healing property can be attributed to the abundantdynamic hydrogen bonds within the elastomer material and the low glasstransition temperature (Tg) (<0° C.) of the PDMS backbone (see, e.g.,FIG. 11).

As previously described, the self-healing of the elastomer material(e.g., PDMS-MPU_(0.4)-IU_(0.6)) is water-insensitive. When the severedpolymer film is healed in water for 24 hours, the resulting film can bestretched up to 1,100 percent strain (see, e.g., FIGS. 3K-3M and FIGS.12A-12E). Importantly, there is no significant water uptake into thepolymer film (see, e.g., 12A-12E). It is believed that thehydrophobicity of the polymer backbone (PDMS) may increase the enthalpygain for hydrogen bonding formation, which is responsible forself-healing. The resulting enthalpy gain may exceed entropy gain byhydration of hydrogen bonding units (which will lead to self-healingfailure). Such elastomers can be used for water-insensitive self-healingpolymers based on broadly used hydrogen bonding systems.

The mechanical and self-healing properties of the elastomer material(e.g., PDMS-MPU_(0.4)-IU_(0.6)) in accordance with the presentdisclosure, allows the material to be processed in various ways. Exampleprocessing includes solution processing or molding and bonding atelevated temperatures and even room temperature (see, e.g., FIGS.13A-13B). For example, two sheets of PDMS-MPU_(0.4)-IU_(0.6) films canbe bonded together giving mechanical properties similar as the bulk film(see, e.g., FIGS. 14A-14F). Further, PDMS-MPU_(0.4)-IU_(0.6) blocks canbe readily attached to PDMS-MPU_(0.4)-IU_(0.6) substrate with robustinterface even under large applied biaxial strain (see, e.g., FIGS. 4Aand 14A-14F). Additionally, using the elastomer material,three-dimensional (3D) self-healable objects can be formed, such asself-healing flower and boat (see, e.g., FIG. 4B and FIGS. 14A-14F).Moreover, the tough self-healing film can be sutured on soft animal skinsurfaces without rupturing (see, e.g., FIGS. 4C-4D). Combing with itsself-healing property in water, this material is especially useful as asubstrate for attaching electronics onto soft surfaces (see, e.g., FIG.4E).

FIG. 1C illustrates examples of different chemical structures ofpolymers synthesized and characterized herein. Further details ofprocesses for synthesizing the various polymers is provided herein.

FIG. 1D illustrates a simulated dimer model of MPU-MPU 108 (top) andIU-IU 110 (bottom), respectively. Calculations for example experimentalembodiments can be performed with the Gaussian 09 program package, wherestructural optimizations are carried out at the B31YP/6-31g(d) levelfollowed by frequency calculation at the same level, affording thestructures on the next page with zero imaginary frequencies. For MPU-MPUinteraction, a maximum of four hydrogen bonds can form. By contrast, IUcan form a maximum of two hydrogen bonds with a counter IU. Accordingly,this supports that the MPU-MPU interaction is stronger than IU-IUinteraction and imparts elasticity. Particularly, the IU-IU dimer modelcan be unstable due to its dynamic motion.

Although the embodiments described above, such as those illustrated byFIGS. 1A-1D, illustrate a polymer backbone with two moieties that eachform hydrogen bonds, embodiments are not so limited. For example, thepolymer backbone can include more than two moieties and/or one or moreof the two or more moieties can form dynamic bonds other than hydrogenbonds, such as metal-ligand bonding, guest-host interactions, and/orsupramolecular interactions. Additional examples of moieties andresulting dynamic bonds are further illustrated herein by FIG. 2G andFIG. 2H.

FIGS. 2A-2H illustrate example properties of polymer films formed usingthe elastomer material, in accordance with various embodiments. FIG. 2Ais a schematic of a stretched polymer film in accordance withembodiments. FIG. 2B illustrates a notched polymer film (e.g., thetoughness of the film) and FIG. 2C illustrates self-healing of thepolymer film in accordance with various embodiments.

FIG. 2D illustrates an example dynamic bonding combinations for strongbond and weak bond, respectively. As previously described, a variety ofdifferent flexible polymer backbones and different types of moieties220, 224 (e.g., bonding units) can be used. Example flexible polymerbackbones 226 include polydimethylsiloxane (PDMS) polyethyleneoxide(PEO), Perfluoropolyether (PFPE), polybutylene (PB),poly(ethylene-co-1-butylene), poly(butadiene), hydrogenatedpoly(butadiene), polybutylene, poly(ethylene oxide)-poly(propyleneoxide) block copolymer or random copolymer, and poly(hydroxyalkanoate).

FIG. 2E illustrates examples of different types of flexible polymerbackbones. As illustrated, the polymer backbone can include PDMS, PEO,Polyethylene, PFPE, PB, poly(ethylene-co-1-butylene) and/orPolydimethylsiloxane, among other types of polymer backbones, such aspoly(butadiene), hydrogenated poly(butadiene), polybutylene,poly(ethylene oxide)-poly(propylene oxide) block copolymer or randomcopolymer, poly(hydroxyalkanoate).

FIG. 2F illustrates different types of moieties 230, 232, 234, which canalso be referred to as bonding sites. The different moieties 230, 232,234 can have different strengths of crosslinking.

In accordance with a number of embodiments, various methods are directedto forming the elastomer material and/or polymer film. An example methodincludes selecting a ratio of at least a first moiety and a secondmoiety based on one or more designated mechanical properties. Aspreviously described, the particular ratio can be selected to setmechanical properties of the resulting polymer film. For example, adecrease in the first moiety increases a fracture strain and decreasesthe Young's modulus and fracture energy. An increase in the first moietyincreases the Young's modulus and fracture energy of the polymer film.The method further includes forming a viscous solution that includes aflexible polymer and the ratio of the at least first moiety and thesecond moiety, and from the viscous solution, forming a polymer filmincludes a supramolecular network of elastomer material. As previouslydescribed, the elastomer material has a flexible polymer backbone thatincludes the flexible polymer with the particular ratio of the at leastfirst moieties and second moieties. The first moieties provide a firstnumber of dynamic bonds resulting from interactions between the firstmoieties and the second moieties provide a second number of dynamicbonds resulting from interactions between the second moieties, with thesecond number of dynamic bonds having a weaker bonding strength than thefirst number of dynamic bonds. The formed polymer film exhibitsautonomous self-healing, a particular Young's modulus, and stretchingbased on the selected ratio of first moieties and second moieties. Forexample, the polymer film can exhibit a Young's modulus of between 0.1and 3.0 MPa, and stretching between 1,200 and 3,000 percent. In a numberof embodiments, the polymer film is severed and the method furtherincludes healing the severed polymer film in water (e.g., for 24 hours),wherein the healed polymer film can be stretched up to 1,100 percentwithout rupturing.

FIG. 2G illustrates examples of different moieties and dynamic bonding,in accordance with various embodiments. The dynamic bonding can becovalent or non-covalent, such as hydrogen bonding, metal-ligandbonding, guest-host interaction, and supramolecular interaction.

FIG. 2H illustrates examples of different moieties and tuning ofrespective dynamic bonding strength, in accordance with variousembodiments. In accordance with various embodiments, the polymerbackbone can include three or more different moieties. In specificembodiments, the three (or more) moieties can be selected from thoseillustrated by FIGS. 2D, 2F, and 2G-2H. At least two of the three ormore different moieties have the different crosslinking dynamic bondingstrength. The third (or more) moieties can have a similar crosslinkingdynamic bonding strength as one of the first or second moieties or adifferent strength, such as a bonding strength that is between thebonding strength of the first moieties and the second moieties.

FIGS. 3A-3N illustrate example properties of polymer films formed usingthe elastomer material, in accordance with various embodiments.

FIGS. 3A-3B illustrate an example of the stretchability of polymerfilms, in accordance with various embodiments. In specific exampleembodiments, the polymer films can be stretched to sixteen times itsoriginal length at a loading rate of 20 mm/min (200 percent/min) withoutrupturing. In more specific embodiments, the polymer films can bestretched up to 3,000 percent. Mechanical and self-healing properties ofPDMS-MPUx-IU1-x polymer film. For example, FIG. 3A illustratePDMS-MPU_(0.2)-IU_(0.8) polymer film before stretching and FIG. 3B showsstretchability at 3,000 percent stretching in an Instron machine.

FIGS. 3C-3D illustrate different stress-strain curves of the filmsprepared with PDMS-MPU (blue), PDMS-IU (orange) andPDMS-MPU_(0.4)-IU_(0.6) (red) with a sample width of 5 mm, thickness of0.4-0.5 mm and length of 10 mm at a loading rate of 20 mm min⁻¹.Stress-strain curves of the films prepared with PDMS-MPU_(0.2)-IU_(0.8)(blue), PDMS-MPU_(0.3)-IU_(0.7) (orange) and PDMS-MPU_(0.4)-IU_(0.6)(red) with a sample width of 5 mm, thickness of 0.4-0.5 mm, length of 10mm and loading rate of 20 mm min⁻¹. As illustrated, the Young's modulusof the PDMS-MPU film can be measured to be 0.98 MPa from its low-strainregion and its strain at break is 750 percent. In contrast, PDMS-IU filmis not elastic and can undergo continuous plastic deformation uponapplied strain. Further, as described above, the polymer films can bestretched up to 3,000 percent.

The mechanical properties of PDMS-MPU-IU can depend on the ratio of thedifferent crosslinked units or types of moieties, such as the MPU and IUunits. In various experimental embodiments, when the ratio of MPU unitsin the polymer is decreased, the fracture strain of the polymer film isincreased, and the Young's modulus and fracture energy are decreased(see FIGS. 3C-3D, as well as Table 1 below). In various related andexperimental embodiments, a comparison of the polymer films illustratedby FIG. 1B can be made. For example:

TABLE 1 Young's Strain Fracture Self-healing modulus at break energyEfficiency (%) (MPa)_(a) (%)_(a) (J/m₂)_(b) after 48 h_(c) PDMS-IU 0.12± 0.03 NA NA NA PDMS-MPU 0.98 ± 0.13  728 ± 104 1331 ± 130 17 ± 5PDMS-MPU_(0.3)-IU_(0.7) 0.43 ± 0.08 2182 ± 180 5730 ± 190 86 ± 8PDMS-MPU_(0.4)-IU_(0.6a) 0.62 ± 0.06 1735 ± 107 11480 ± 710   72 ± 12PDMS-MPU_(0.5)-IU_(0.5) 0.71 ± 0.11 1475 ± 129 8803 ± 380  41 ± 11 PDMS(Sylgard 184) 0.41 ± 0.10 170 ± 15  84 ± 12 NA Polyurethane 1.73 ± 0.13710 ± 30 2280 ± 410 NA (SG80A) SEBS 3.83 ± 0.31 330 ± 20 1360 ± 200 NA

For above described table, the sample size is 5 mm (width), 10 mm (gaugelength) and 0.4-0.5 (thickness); Stretching speed: 50 mm/min. For b thesample size is 40 mm (width), 5 mm (gauge length) and 0.4-0.5(thickness); 20 mm single-edge notch; Stretching speed: 50 mm/min.Self-healing experiments are done at ambient temperature on Teflonsubstrate. Error bars show standard deviation; sample size n=5.Mechanical properties of PDMS (Sylgard 184), Polyurethane (SG80A) andSEBS are characterized as well. Thermoplastic polyurethane (SG80A) andSEBS films are prepared on OTS-treated substrate from chloroformsolution and toluene solution, respectively.

The Young's modulus of the PDMS-MPU film can be measured to be 0.98 MPafrom its low-strain region and its strain at break is 750 percent (see,e.g., FIG. 3C and Table 1). In contrast, PDMS-IU film is not elastic andcan undergo continuous plastic deformation upon applied strain (see,e.g., FIGS. 3C-3D and Table 1). The MPU units are able to form quadruplehydrogen bonding in a cooperative manner with counter MPU units whereasthe IU units can only form maximum dual hydrogen bonding with another IUunit due to the steric hindrance from the isophorone moieties (see,e.g., FIGS. 3E-3F and as further illustrated by FIG. 1C). Themultivalent effect hence results in MPU-MPU interaction being muchstronger than IU-IU interaction, such that the MPU-MPU crosslinking canbetter hold the elastomer together to impart elasticity. As may beappreciated, embodiments are not limited to hydrogen bonding, to twodifferent types of moieties and/or to moieties that exhibit four dynamicbonds and two dynamic bonds. The polymer backbones, in accordance withthe various embodiments and variations described herein, have two (ormore) different moieties. At least two of the different moieties exhibitdifferent strength dynamic bonding, one of which is easier to break.

FIGS. 3E-3F illustrate an experimental example of the notchinsensitivity of the polymer film. For example, FIG. 3E illustrates anotched-PDMS-MPU_(0.4)-IU_(0.6) polymer film before stretching and FIG.3F illustrates after 1,200 percent stretching in an Instron machineshowing that the film is notch-insensitive.

The polymer films, surprisingly, are able to achieve notch-insensitivestretching up to 1,200 percent strain, demonstrating their toughness.Other previously formed and typical PDMS substrates rupture at less than200 percent strain (see, Table 1). The MPU units are able to formquadruple hydrogen bonding in a cooperative manner with counter MPUunits whereas the IU units can only form maximum dual hydrogen bondingwith another IU unit due to the steric hindrance from the isophoronemoieties (as further illustrated by FIG. 1C).

FIG. 3G illustrates the fracture energy of the polymer film with thenotch as illustrated by FIGS. 3E-3F. More specifically FIG. 3Gillustrates the fracture energy as a function of molar ratio of MPU andIU units in polymer (PDMS-MPUx-IU1-x., blue) and blended film (PDMS-MPUand PDMS-IU, red). Moreover, since the MPU and IU units are covalentlylinked by flexible PDMS, the above process can synergistically takeplace.

FIG. 3H illustrates example stress-strain curves of a polymer filmhealed at room temperature (r.t.) for different lengths of time showingan increase of the stretching ability when the film is allowed to healfor longer. In specific embodiments, the healed polymer film is againstretched to 1,500 percent after 48 hours with self-healing efficiencyof 78 percent.

FIGS. 3I-3J illustrate an example of a polymer film self-healing at roomtemperature. More specifically, FIGS. 3I-3J include optical microscopeimages of damaged and healed PDMS-MPU_(0.4)-IU_(0.6) film showingdisappearance of the scar after healing at 20° C. for 3 days. Asillustrated, the scar on a cut polymer film (PDMS-MPU_(0.4)-IU_(0.6))almost disappears after healing at room temperature for three days

FIGS. 3K-3M illustrate an example of a polymer film self-healing in thepresence of water. Self-healing of THE PDMS-MPU_(0.4)-IU_(0.6) film caneven take place under water. A PDMS-MPU_(0.4)-IU_(0.6) film can bebisected to two pieces, stained by pink and blue ink from color pen,respectively and as illustrated by FIG. 3K, and put together under waterfor self-healing, as illustrated by FIG. 3L. After 24 hours, the polymerfilm is stretched as illustrated by FIG. 3M. In specific experimentalembodiments, when the severed polymer films is healed in water for 24hours, the resulting film can be stretched up to 1,100 percent strain.

FIG. 3N illustrates an example comparison of the polymer material toother types of material. As illustrated, the polymer films exhibitsnotch-insensitive stretching and a high fracture energy (around 12,000J/m2) among reported intrinsically tough materials as well asself-healing polymers.

A number of embodiments are directed to a polymer films formed of aflexible polymer backbone (with low transition temperature) having aparticular ratio of a first moieties (e.g., provide strong dynamicbonding) and a second moieties (e.g., weak bonding) that has a lowercrosslink dynamic bonding strength than the first moieties. The polymerbackbone can include PDMS, PEO, PFPE, PB, poly(ethylene-co-1-butylene),poly(butadiene), hydrogenated poly(butadiene), polybutylene,poly(ethylene oxide)-poly(propylene oxide) block copolymer or randomcopolymer, and poly(hydroxyalkanoate), among other types of flexiblepolymer backbones. The resulting polymer film can be stretchable,self-healable, and mechanically tough. For example, the polymer film canexhibit a Young's Module that is tunable from 0.1 MPa to 3.0 MPa (and inspecific embodiments, from 0.1 to 1.5 MPa). The stretching range of thepolymer film when un-notched can have a strain at break of up to 3,000percent (which is also the fracture strain) and when notched can have astrain at break of up to 2,000 percent. The fracture energy can be up to15,000 J/m². In some embodiments, the first moieties can provide anumber of dynamic bonds resulting from interactions between the firstmoieties and that have a crosslinking strength that is at least twotimes higher than a crosslinking strength of the second moieties. Forexample, the strength of MPU-MPU is at least two times higher than thatof IU-IU since MPU-MPU has two more H-bonds than IU-IU. Thetransmittance of the polymer film can be at least (or around) 98 percentin the range of 400 nm-1000 nm. The self-healing efficiency of thepolymer film can depend on healing temperature and time. At 25° C., asan example, self-healing efficiency can be reached to 75 percent after48 hours. At 60° C., self-healing efficiency can be reached to almost100 percent after 6 hours.

Experimental/More Detailed Embodiments

Various embodiments are directed to a supramolecular stretchable, toughand self-healable polymer film, constructed via a mixture of strong andweak crosslinking dynamic bonds. The resulting polymer possesses acombination of exceptional mechanical properties, e.g., stretchability,toughness and autonomous self-healability in water. This uniquecombination of properties enables fabrication of a variety of 2D and 3Dstructures, capacitive strain sensing e-skin and stretchable modularelectronic systems with high toughness, stretchability and robustnessagainst damage. The molecular design is simple and is applicable tovarious polymer structures.

In various specific experimental embodiments, the PDMS-MPUx-IU1-xpolymer films can be formed by dissolving 3-5 grams (g) ofPDMS-MPUx-IU1-x in 15 mL-20 mL CHCl₃ and stirred at 50° C. Resultantviscous solution are stirred for more than three hours and waresubsequently gradually cooled down to room temperature. The resultantsolution is poured onto OTS-treated silicon substrates (e.g., fourinches) and dried at room temperature for six hours followed by dryingat 80° C. under reduced pressure (about 100 torr) for three hours.Polymer films are then peeled off after cutting in certain dimensionsand ready for mechanical testing.

The resulting polymer films can be tested to identify various propertiesof the films. Mechanical tensile-stress experiments can be performedusing an Instron 5565 instrument. At least three samples are tested foreach type of polymer film. Tensile experiments are performed at ambientconditions with samples with width of five mm, thickness of around 0.5mm, length of ten mm and controlled strain-rate of twenty mm/mm. Fordetermination of fracture energy, the procedures of pure-shear test isdescribed by Ducrot, E. et al., “Toughening elastomers with sacrificialbonds and watching them break,” Science 344, 186-189 (2014) and Sun, J.Y. et al., “Highly stretchable and tough hydrogels,” Nature 489, 133-136(2012), each of which are incorporated herein in their entirety fortheir teachings. A sample with a length of five mm, a thickness of 0.5mm, and a width of forty mm can be used. For a notched sample, a notchof twenty mm length is made in the middle of a strip of film with astrain-rate of fifty mm/mm. For self-healing tests, the polymer filmsare cut into two pieces and then the cut surfaces are put in contact.The polymer films are then healed at room temperatures for differentperiods. The healed polymer films are then stretched. The healingefficiency can be defined as the ratio of strain at break between healedfilm and original film. Values of the Young's modules, maximum strain atbreak, and healing efficiencies are determined according to data of atleast three trials.

For various experimental and more detail embodiments, Bis(3-aminopropyl)terminated poly(dimethylsiloxane) (H₂N-PDMS-NH₂, Mn=5000-7000) ispurchased from Gelest. The remaining chemicals and solvents arepurchased from Sigma-Aldrich. All chemicals used as received withoutfurther purification. NMR (¹H and ¹³C) spectra can be recorded on aVarian Mercury 400 NMR spectrometer in deuterated solvents at roomtemperature. Infrared spectra are recorded with a Horiba Jobin-YvonFluorolog-3 fluorometer. Absorption spectra were recorded on an AgilentCary 6000i UV/Vis/NIR Spectrophotometer. Analytical gel permeationchromatography (GPC) experiments can be performed on a Malvern VE2001GPC solvent/sample Module with three ViscoGEL™ IMBHMW-3078 columns. Thecalibration can be based on polystyrene standards with narrow molecularweight distribution. Differential Scanning Calorimetry (DSC) experimentsare performed using a Model Q2000 from TA Instruments. The temperaturerange can be −90 to 150° C., at a heating and cooling speed of 10°C./min. Dynamic mechanical analysis measurement is carried out ondynamic mechanical Analyzer TA Instrument Q800 (strain rate of 0.01mm/mm; frequency sweeps at 0.1-10 Hz; Temperature: −90-10° C.).Viscosity measurements can be carried out on an Ares G2 rheometer withan Advanced Peltier System (APS) as the bottom plate and a 40 mm cone asthe top geometry. The shear rate sweep is performed from 1 l/s to 1000l/s. All solutions are Newtonian. The chips for modular electronics areordered from Mouser electronics.

In specific experimental embodiments, the PDMS-MPU_(0.4)-IU_(0.6)polymer can be synthesized by adding Et₃N (10 mL) to a solution ofH₂N-PDMS-NH₂ (100 g, Mn=5000-7000, 1 eq) in anhydrous CHCl₃ (400 mL) at0° C. under argon atmosphere. After stirring for 1 hour, a mixturesolution (CHCl₃) of 4,4′-Methylenebis(phenyl isocyanate) (2.0 g, 0.4 eq)and Isophorone diisocyanate (2.7 g, 0.6 eq.) is added dropwise. Theresulting mixture is stirred for 1 hour while the temperature is kept at0° C. with ice water. The solution is then allowed to warm to roomtemperature and stirred for 4 days. After reaction, MeOH (15 mL) isadded for complete removal of remained isocyanate and stirred for 30minutes. Then, solution is concentrated to ½ of its volume and 60 mLMeOH is poured into it to precipitate. White precipitate-like viscousliquid appeared and the mixture is settled for 30 minutes. The upperclear solution is then decanted. 100 mL CHCl₃ is added to dissolve theproduct. The dissolution-precipitation-decantation process is repeatedfor three times and the final product is subjected to vacuum evaporationto remove the solvent and trace of Et₃N. A yield of 65 g (63 percent) isobtained with a molecular weight according to GPC of: Mw=103,400;Mn=65,000 (Ð=1.6)¹H NMR (400 MHz, d5-THF): δ 7.33 (d, J=8.0 Hz, 4H),6.97 (d, J=8.0 Hz, 4H), 3.77 (s, 2H), 0.01 (b, 1325H). ¹³C NMR (400 MHz,CDCl₃): δ 158.78, 139.18, 137.31, 125.34.

As previously discussed and illustrated by FIG. 1B, PDMS-MPU, PDMS-IU,PDMS-MPU_(0.2)-IU_(0.6), PDMS-MPU_(0.3)-IU_(0.7), andPDMS-MPU_(0.5)-IU_(0.5) are synthesized using different mixing molarratio of 4,4′-Methylenebis(phenylisocyanate) and Isophorone diisocyanateaccording to the same procedure as that used forPDMS-MPU_(0.4)-IU_(0.6). For PDMS-MPUx-IU1-x, mixture of4,4′-Methylenebis(phenyl isocyanate) (x eq) and Isophorone diisocyanate(1-x eq.) is used.

For PDMS-MPU, in various experimental embodiments, resulting molecularweight according to GPC includes: Mw=99,000; Mn=71,000 (Ð=1.4)¹H NMR(400 MHz, d5-THF): δ 7.33 (d, J=8.0 Hz, 4H), 6.97 (d, J=8.0 Hz, 4H),3.77 (s, 2H), 0.01 (b, 520H). For PDMS-IU resulting molecular weightaccording to GPC include: Mw=123,000; Mn=68,000 (Ð=1.8)¹H NMR (400 MHz,CDCl₃): δ 7.15 (b, 2H), 6.91 (b, J=8.0 Hz, 2H), 3.48 (d, J=9 Hz, 4H),1.71 (m, 4H), 0.63 (d, J=9 Hz, 4H), 0.01 (b, 545H). ForPDMS-MPU0.2-IU0.8 resulting molecular weight according to GPC include:Mw=112,000; Mn=84,000 (Ð=1.3) ¹H NMR (400 MHz, d5-THF): δ 7.33 (d, J=8.0Hz, 4H), 6.97 (d, J=8.0 Hz, 4H), 3.77 (s, 2H), 0.01 (b, 2531H). ForPDMS-MPU0.3-IU0.7 resulting molecular weight according to GPC includes:Mw=116,000; Mn=73,000 (Ð=1.6)¹H NMR (400 MHz, d5-THF): δ 7.33 (d, J=8.0Hz, 4H), 6.97 (d, J=8.0 Hz, 4H), 3.77 (s, 2H), 0.01 (b, 1633H). ForPDMS-MPU_(0.5)-IU_(0.5) resulting molecular weight according to GPCincludes: Mw=99,000; Mn=69,000 (Ð=1.4)¹H NMR (400 MHz, d5-THF): δ 7.33(d, J=8.0 Hz, 4H), 6.97 (d, J=8.0 Hz, 4H), 3.77 (s, 2H), 0.01 (b,1011H).

FIGS. 4A-4O illustrate example properties of films formed using theelastomer material, in accordance with various embodiments.

FIG. 4A illustrates an example of a film formed of different coloredtiles, as further described herein in connection with FIGS. 14A-14F.PDMS-MPU_(0.4)-IU_(0.6) blocks can be readily attached toPDMS-MPU_(0.4)-IU_(0.6) substrate with a robust interface even under(large) applied biaxial strain. To generate a self-healing thermoplasticelastomer for a self-healable electronic skin, in accordance with anexperimental embodiment, twenty-five pieces of film blocks are preparedwith five different colors. The blocks are attached to aPDMS-MPU_(0.4)-IU0.6 film substrate and allowed to bond at roomtemperature for 6 hours with a gently applied pressure. The resultingpatterned film is biaxially stretched without any delamination.

FIG. 4B illustrates an example of a 3D structure formed using theelastomer material, in accordance with various embodiments. Morespecifically, FIG. 4B is an optical image of a flower made by bondingvarious pieces at 50° C. with a green LED (left) and schematicillustration of 3D assembly for flower (inset). The leaves were stainedby alkylated-DPP dye.

FIGS. 4C-4D illustrate examples of the ability to suture theself-healing polymer film onto animal skin surfaces without rupturingthe polymer film, in accordance with various embodiments. For example,FIG. 4C illustrates an optical image of suturing test of PDMS Sylgard184 on a pig inner skin and FIG. 4D illustrates an optical image ofsuturing PDMS-MPU_(0.4)-IU_(0.6) film on pig inner skin. Red arrowsindicated rupture of PDMS due to its poor fracture toughness while theexceptional toughness of PDMS-MPU_(0.4)-IU_(0.6) results in successfulsutures that are robust and stable even under stretching.

FIG. 4E illustrates an example of the self-healing polymer film suturedon the surface of pig skin, in accordance with various embodiments. Thepolymer can be used to form various electronics. For example, sensingcircuitry, such as a temperature senor, strain sensor, capacitancesensor and other types of sensor can be formed using the polymer film.FIG. 4E illustrates a temperature sensor formed using the self-healingpolymer film and that is then sutured on a surface of pig skin.Temperature changes can be induced by a heat gun in experimentalembodiments. Combing with its self-healing property in water, thismaterial is especially useful as a substrate for attaching electronicsonto soft surfaces.

FIGS. 4F-4H illustrate an example of a self-healable electrode formedusing the elastomer material, in accordance with various embodiments.For example, FIG. 4F is a schematic illustration of self-healingelectrode. FIG. 4G illustrates an optical image of self-healingelectrode equipped with an LED lamp before stretching and FIG. 4Hillustrates an optical image of the self-healing electrode afterstretching.

Taking advantage of these features, various experiment embodimentsinclude the fabrication of stretchable and autonomous self-healingelectrodes with liquid metal EGaIn as a conductive layer andPDMS-MPU_(0.4)-IU_(0.6) as the encapsulation and supporting layer EGaIncan be used for fabricating stretchable and self-healing electrodes.Encapsulation of EGaIn in PDMS as a layer form is challenging due topoor wetting of the polar EGaIn liquid on the highly hydrophobic PDMSsurface. In contrast, EGaIn exhibits good wetting properties onPDMS-MPU_(0.4)-IU_(0.6) films, which is believed to be due to theinteractions between urea groups and native oxide layer (see, e.g.,FIGS. 15A-15B, 16, and 17A-17B). This electrode exhibits highstretchability (e.g., at least 500 percent) with stable (e.g., at least100 cycles) and low resistance (see, e.g., FIGS. 4G-4I). Importantly,this electrode is self-healable, i.e. can be repeatedly connected aftercutting, at room-temperature.

The self-healing electrode can be fabricated by taking advantage of themoldable feature of the polymer at high temperature and its bondingproperty. A wafer-sized polymer film with 0.8 mm thickness onOTS-treated silicon substrate is prepared. The polymer film on substrateis pressed by Teflon mold at 80° C. and allowed to rest for two hours.Then, after removing the Teflon mold, successful patterns with periodicpolymer walls are confirmed and liquid metal alloy (EGaIn) is bladedonto the pattern by using small piece of polymer film and other polymerfilm with 0.3 mm thickness is subsequently put on patterned film withliquid metal as an encapsulation layer. The bonding process involvesannealing at room temperature for six hours after applying gentlepressure to keep the two pieces in good contact; robust self-healingelectrode can be obtained with a stable interface. Gentle pressure, asused herein, can include or refer to around 1 kilopascal (kPa) ofpressure and/or a pressure sufficient to make physical contact betweentwo films. The electronic skin is fabricated by sandwiching a dielectriclayer with two self-healing electrodes, in which the thickness of thedielectric layer is 330 μm.

In a number of experimental embodiments, the electrode is cut. When theelectrode is cut into two pieces and put together for self-healing, theelectrical conductivity can recover instantaneously when two brokenpieces are put in contact. After nine hours of healing at ambientcondition, the electrical and mechanical properties of the self-healedelectrode are almost identical to the original one (see, e.g., FIGS.18A-18D). Furthermore, the electrode can be molded into 3D structuresowing to its thermoplastic property (see, e.g., FIG. 4J). Accordingly,various embodiments are directed to an ambient self-healing electrodeformed of an elastomer in accordance with the various embodiments. Theambient self-healing electrode exhibits a stretchability of at least 500percent and can be up to 1,200 percent and low resistance of around 3ohm, although the electrical resistance can depend on the dimension ofthe conductive line and can be observed to be a stable and reversibleresistance of up to 500 percent (see, e.g., FIG. 4I and FIGS. 18A-18D).

FIG. 4I illustrates an example of electrical resistance as a function ofstrain with self-healing electrode and electrical resistance undercyclic stretching, in accordance with various embodiments.

FIG. 4J illustrates an example of molding a self-healable electrode, inaccordance with various embodiments. For example, the optical imagesshow the possibility to change shape of the self-healing electrode bytaking advantage of its thermoplastic property. The self-healingelectrode has a flat linear shape (top). It is wrapped around a rod(middle) and is held at this configuration at 50° C. for 30 minutes.After removal of the rod, the electrode maintains the helical shapewithout the template (bottom).

In other experimental and more detailed embodiments, a fullyself-healing e-skin (capacitive strain sensor) is demonstrated whichexhibits high resistance to constant mechanical damage and complete roomtemperature self-healability even after complete cutting (see, e.g.,FIGS. 4H, 19A-19C, 20, 21A-21B, and 22A-22C).

FIG. 4K illustrates an example of a self-healable capacitive strainsensor formed using the elastomer material, in accordance with variousembodiments. A strain sensor can be fabricated by bonding twoself-healing electrodes, as described above in connection with FIGS.4F-4H. For example, as illustrated by the right side of FIG. 4K, aself-healable capacitive strain sensor can be formed by preparing twoelectrodes, attaching a dielectric layer to one of the electrodes, andattaching the other electrode as a counter electrode resulting thesandwich structure illustrated by the left side of FIG. 4K. In specificembodiments, the strain sensor is fabricated based on bonding betweenlayers through the stack and annealing at room temperature for at leastsix hours.

FIG. 4L illustrates an example a self-healing of the capacitive strainsensor illustrated by FIG. 4K, in accordance with various embodiments.More specifically, FIG. 4L includes optical images of the cut strainsensor (inset) and that the healed strain-sensor maintains highstretchability, such as up to 500 percent for sensing that is reversibleand stable. By increasing the healing time, the healed strain-sensor canstably operate at up to 400 percent strain.

FIG. 4M illustrates example electrical capabilities of a self-healedsensor as compared to a pristine sensor, in accordance with variousembodiments. As illustrated, the capacitance change remains relativelythe same when comparing stretching of an original (has not self-healed)sensor and with a healed sensor after damaged (e.g., 9 hours afterhealing).

Various embodiments include forming an array of strain sensors, aspreviously described. FIG. 4N illustrates and example of a strain sensorarray, in accordance with various embodiments. For example, FIG. 4Nillustrates an optical image of a 7×7 strain-sensor array detecting thepresence of a metal ball.

FIG. 4O illustrates the strain distribution as illustrated by FIG. 4N,in accordance with various embodiments. More specific, illustrated is amap of the strain distribution based on the change in capacitance by theweight of the metal ball (e.g., around 30 g in weight).

FIGS. 5A-5B illustrate transmittance of an example polymer film, inaccordance with various embodiments. FIG. 5A illustrates an opticalimage of PDMS-MPU_(0.4)-IU_(0.6). FIG. 5B illustrates transmittance ofthe PDMS-MPU_(0.4)-IU_(0.6) polymer film illustrated by FIG. 5A in thewavelength range of 400-1000 nm. The example polymer film (e.g., a 0.55mm thick polymer film) shows a 98 percent average transmittance in thevisible range, illustrating that the polymer film is transparent withhigh optical quality.

FIG. 6 illustrates an experimental results of testing the notchsensitivity and stretchability of an example polymer film, in accordancewith various embodiments. A notch (5 mm×5 mm) is made in aPDMS-MPU_(0.4)-IU_(0.6) polymer film with 0.5 mm thickness, 15 mm lengthand 15 mm width (left) and the film is stretched at the loading rate of50 mm/min. The notch is blunted and remain stable (middle and right).

FIGS. 7A-7B illustrate example stress curves of an example polymer film,in accordance with various embodiments. For example, the stress-straincurves illustrated by FIGS. 7A-7B are of a PDMS-MPU_(0.4)-IU_(0.6)polymer film under cyclic stress-strain curve (up to 500 percent strain)at first loading (black) and second loading (blue) after 30 minutesrest, as illustrated by FIG. 7A, cyclic stress-strain curve (up to 1,000percent strain) at first loading (black) and second loading (blue) after30 minutes rest, as illustrated by FIG. 7B. The polymer film has athickness of 0.53 mm, length of 10 mm and width of 5 mm is stretched ata loading rate of 50 mm/min.

FIGS. 8A-8B illustrate example stress applied to a notched polymer filmand unnotched polymer film, in accordance with various embodiments. FIG.8A illustrates the geometry of unnotched and notched samples for pureshear test. The sample thickness can be b₀=0.52 mm. FIG. 8B illustratesthe resulting tress-extension curves of the unnotched and notchedPDMS-MPU_(0.4)-IU_(0.6) polymer film. The fracture energy is calculatedas U(L_(c))/(a₀×b₀). Le is the distance between the clamps when crackstarts to propagate.

FIGS. 9A-9B illustrate example viscosity of polymer films, in accordancewith various embodiments. For example, FIG. 9A illustrates viscositymeasurements of PDMS-MPU, PDMS-MPU_(0.4)-IU_(0.6),PDMS-MPU_(0.3)-IU_(0.7) and PDMS-IU with various concentrations inCHCl₃. As the MPU portion increases in the polymer, viscosity of samplesincreases because of formation of MPU-MPU bond in solution.Concentration dependency shows non-linearity in viscosity. FIG. 9B is aschematic illustration of the self-assembly process of PDMS-MPU-IU fromsolution to solid state.

FIGS. 10A-10E illustrate example spectrometry results of various polymerfilms, in accordance with various embodiments. FIG. 10A illustrates aproton NMR spectrum of PDMS-MPU in CDCl₃ (80 percent)+MeOD (20 percent).FIG. 10B illustrates a proton NMR spectrum of PDMS-IU in CDCl₃. FIG. 10Cillustrates a proton NMR spectrum of PDMS-MPU_(0.4)-IU_(0.6) in CDCl₃.FIG. 10D illustrates a proton NMR spectrum and FIG. 10E illustrates a 2DNMR spectrum of PDMS-MPU_(0.4)-IU_(0.6) in CDCl₃ (80 percent)+MeOD (20percent) at concentration of 50 mg/ml. In CDCl₃, as illustrated, peaksof MPU units are not seen, suggesting that polymer chains arepre-crosslinked in solution state. Upon the addition of MeOD to disrupthydrogen-bonding, MPU peaks are observed. 2D COSY NMR support the protonpeak assignments.

FIG. 11 illustrates an example differential scanning calorimetry (DSC)thermal analysis of PDMS-MPU_(0.4)-IU_(0.6) (red),PDMS-MPU_(0.3)-IU_(0.7) (orange) and PDMS-MPU_(0.2)-IU_(0.8) (blue), inaccordance with various embodiments.

FIGS. 12A-12E illustrates an example of self-healing of a polymer filmin the presence of water, in accordance with various embodiments. Asillustrated by FIGS. 12A and 12B, a PDMS-MPU_(0.4)-IU_(0.6) polymer filmis bisected to two pieces. FIG. 12C illustrates that the polymer film isin the presence of water and the two pieces are put together under waterfor self-healing. After 24 hours, as illustrated by FIG. 12D, thepolymer film is stretched. FIG. 12E illustrates the examplestress-strain curve of the self-healed polymer film underwater.

FIGS. 13A-13B illustrate an example dynamic mechanical analysis ofPDMS-MPU_(0.4)-IU_(0.6) polymer film, in accordance with variousexperimental embodiments. As illustrated by FIG. 13A, frequency sweepingshows that storage modulus is higher than loss modulus at mostfrequencies. FIG. 13B illustrates an example of temperature sweeping ofthe polymer film.

FIGS. 14A-14F illustrate various properties of example polymer films, inaccordance with various embodiments. For example, FIG. 14A illustrates aroom temperature bonding process of two polymer films. TwoPDMS-MPU_(0.4)-IU_(0.6) film pieces are prepared with different colors.One is stained by a pink color and the other is stained by a blue colorfor visualization. The two films are stacked to each other and form astable interface by a simple bonding process (top). The simple bondingprocess involves annealing at room temperature for at least 6 hoursafter applying gently pressure to keep the two pieces in contact. Theresultant polymer film is stretched without any break (bottom). FIG. 14Billustrates an example stress-strain curves of PDMS-MPU_(0.4)-IU_(0.6)film (black) and simple bonded film (blue). FIG. 14C is a schematicillustration of room-temperature bonding process. As previous describedin connection with FIG. 4D, twenty-five PDMS-MPU_(0.4)-IU_(0.6) filmblocks are prepared with five different colors (Pink, Orange, Green,Blue and Black). The blocks are stacked to a PDMS-MPU_(0.4)-IU_(0.6)film substrate and formed stable interface by simple bonding process(e.g., annealing at room temperature for at least 6 hours after applyinggentle pressure). As illustrated by FIG. 14D, the resultant patternedfilm (left) is stretched without any delamination (right). The simplebonding process, in specific embodiments, includes annealing at 50° C.for 10 minutes and subsequent annealing at room temperature for 12 hoursbefore mechanical testing. FIG. 14E is an optical image of self-healingboat on blue plate and FIG. 14F is optical images of a self-healed boatin water bath and a punctured self-healing boat by sharp blade (inset).

FIGS. 15A-15B illustrate an example of patterning the polymer film usinga mold, in accordance with various embodiments. As illustrated by FIG.15A, PDMS-MPU_(0.4)-IU_(0.6) polymer film can be patterned by Teflonmold at 80° C. under pressure, in which polymer walls are periodicallygenerated. In various embodiments, as illustrated by FIG. 15B, liquidmetal (e.g., EGaIn) is bladed onto the film. Subsequently, it can beencapsulated with another PDMS-MPU_(0.4)-IU_(0.6) polymer film by asimple bonding process (e.g., stacking the layers and heating at 50° C.for 10 min).

FIG. 16 illustrates an example stress cure of PDMS-MPU_(0.4)-IU_(0.6)film (black) and self-healing electrode (blue), in accordance withvarious embodiments.

FIG. 17A illustrates liquid metal exhibited good wetting onPDMS-MPU_(0.4)-IU_(0.6) and FIG. 17B illustrates that the liquid metalcannot be bladed uniformly onto conventional PDMS film because of badwetting, in accordance with various embodiments.

FIGS. 18A-18D illustrate an example experiment of connecting aself-healing electrode to an LED lamp, in accordance with variousembodiments. As illustrated by FIGS. 18A and 18B, the electrode is cut,which results in the LED lamp turning off. After placing the piecestogether and 9 hour self-healing process at room temperature, theelectrode is successfully stretched and LED is on, as illustrated byFIGS. 18C and 18D. Accordingly, the electrode is capable ofroom-temperature mechanical and electrical self-healing.

FIGS. 19A-C illustrate example equipment that can be used to stretch thepolymer film and test the resulting strain, in accordance with variousembodiments. FIG. 19A illustrate an optical image of a strain-sensorformed using the polymer film and as loaded on a stretching station(with zero percent strain). FIG. 19B illustrates an optical image of thestrain-sensor after 500 percent stretching. FIG. 19C illustrates thecapacitance change of the strain-sensor as a function of the strain.

FIG. 20 illustrates an example capacitance change at differentfrequencies and over multiple cycles of stretching the polymer film, inaccordance with various embodiments. More specifically, the capacitancechange in each cycle is illustrated at a frequency of 0.05 Hz (lowfrequency, blue) and 0.5 Hz (high frequency, red) and a maximum 30percent strain. At 0.5 Hz, the decrease of capacitance with stretchingcycle is attributed to the viscoelastic behavior of the strain-sensor.After 100 strain/release cycles and 5 minutes of resting, thestrain-sensor exhibits the same capacitance as the original value.

FIGS. 21A-21B illustrate example of strain-sensors, in accordance withvarious embodiments. For example, FIG. 21A illustrates optical images ofmulti-stage human motion detection by a strain-sensor mounted on humanfinger. The strain-sensor is able to detect human motion clearly andsensitively. FIG. 21B illustrates a cyclic test of human motiondetection from stage 1 to stage 5 without any rest. The strain-sensorexhibits viscoelastic behavior derived from polymer part. Even though itshows 100 percent self-recovery after stretching, it can take at least afew seconds for complete recovery, such that strain-sensing can belimited at high frequency. However, when the sensor is conformallylaminated onto human finger or elastic substrates, such as PDMS, theviscoelastic problem is not observed. To make conformal contact betweensensor and glove, a small amount of ethanol can be utilized, which madesurface of sensor sticky.

FIGS. 22A-C illustrate example equipment that can be used to stretch thepolymer film with a notch and test the resulting strain, in accordancewith various embodiments. FIG. 22A illustrates an optical image of anotched strain-sensor formed using the polymer film and as loaded on astretching station (with zero percent strain). FIG. 22B illustrates anoptical image of the notched strain-sensor after stretching. FIG. 22Cillustrates the capacitance change of the notched strain-sensor as afunction of the strain. The stain-sensor itself can be protected bytough material, so that when damage occurs or is applied, the protectivelayer (polymer layer) prevents the strain-sensor from propagation andallows for stable operation of the strain-sensor even under high strain.Additionally, because of its autonomous self-healing capability, thedamage can completely disappear. In various embodiments, suchstrain-sensors can be utilized in electronic skin that is similar tohuman skin in mechanical properties and sensing capability.

Various embodiments are implemented in accordance with the underlyingProvisional Application (Ser. No. 62/569,236), entitled “Stretchable,Tough, and Self-healing Elastomer and Applications Thereof” filed onOct. 6, 2017, to which benefit is claimed and which is fullyincorporated herein by reference. For instance, embodiments hereinand/or in the provisional application may be combined in varying degreesincluding wholly combined. As an example, the embodiments herein can becombined and/or include the subject matter involving the example ofstretchable, tough, and self-healing elastomers, methods of forming theelastomers, and experimental embodiments illustrating features of theelastomers. Reference may also be made to the experimental teachings andunderlying references provided in the underlying provisionalapplication. Embodiments discussed in the provisional applications arenot intended, in any way, to be limiting to the overall technicaldisclosure, or to any part of the claimed invention unless specificallynoted.

Terms to exemplify orientation, such as top view/side view, before orafter, upper/lower, left/right, top/bottom, above/below, andx-direction/y-direction/z-direction, may be used herein to refer torelative positions of elements as shown in the figures. It should beunderstood that the terminology is used for notational convenience onlyand that in actual use the disclosed structures may be orienteddifferent from the orientation shown in the figures. Thus, the termsshould not be construed in a limiting manner.

As examples, the Specification describes and/or illustrates aspectsuseful for implementing the claimed disclosure by way of variouscircuits or circuitry which may be illustrated as or using terms such asblocks, modules, device, system, unit, controller, and/or othercircuit-type depictions. Such circuits or circuitry are used togetherwith other elements (robotics, electronic devices, prosthetics,processing circuitry and the like) to exemplify how certain embodimentsmay be carried out in the form or structures, steps, functions,operations, activities, etc. For example, in certain of theabove-discussed embodiments, one or more illustrated items in thiscontext represent circuits (e.g., discrete logic circuitry or(semi)-programmable circuits) configured and arranged for implementingthese operations/activities, as may be carried out in the approachesshown in the figures. In certain embodiments, such illustrated itemsrepresent one or more circuitry and/or processing circuitry (e.g.,microcomputer or other CPU) which is understood to include memorycircuitry that stores code (program to be executed as a set/sets ofinstructions) for performing a basic algorithm (e.g., inputting,counting signals having certain signal strength or amplitude,classifying the type of force including a magnitude and direction usingcapacitance values output by the sensor circuitry, sampling), and/orinvolving sliding window averaging, and/or a more complexprocess/algorithm as would be appreciated from known literaturedescribing such specific-parameter sensing. Such processes/algorithmswould be specifically implemented to perform the related steps,functions, operations, activities, as appropriate for the specificapplication.

Based upon the above discussion and illustrations, those skilled in theart will readily recognize that various modifications and changes may bemade to the various embodiments without strictly following the exemplaryembodiments and applications illustrated and described herein. Forexample, methods as exemplified in the Figures may involve steps carriedout in various orders, with one or more aspects of the embodimentsherein retained, or may involve fewer or more steps. Such modificationsdo not depart from the true spirit and scope of various aspects of thedisclosure, including aspects set forth in the claims.

What is claimed is:
 1. An elastomer material comprising: a flexiblepolymer backbone with a particular ratio of at least first moieties andsecond moieties, wherein the first moieties are configured and arrangedto provide a first number of dynamic bonds resulting from interactionsbetween the first moieties; and the second moieties are configured andarranged to provide a second number of dynamic bonds resulting frominteractions between the second moieties, the second number of dynamicbonds having a weaker bonding strength than the first number of dynamicbonds, and wherein the elastomer material, based on the ratio of thefirst moieties and second moieties, exhibits autonomous self-healing, aparticular toughness, and is stretchable.
 2. The elastomer material ofclaim 1, wherein the elastomer material exhibits a Young's modulus ofbetween 0.1 and 3.0 megapascal (MPa) and stretching of between 1,200 and3,000 percent without rupturing, and wherein the dynamic bonds includeat least one selected from the group consisting of hydrogen bonding,metal-ligand bonding, guest-host interactions, and supramolecularinteractions.
 3. The elastomer material of claim 1, wherein the flexiblepolymer backbone is selected from the group consisting of:polydimethylsiloxane (PDMS) polyethyleneoxide (PEO), Perfluoropolyether(PFPE), polybutylene (PB), poly(ethylene-co-1-butylene),poly(butadiene), hydrogenated poly(butadiene), polybutylene,poly(ethylene oxide)-poly(propylene oxide) block copolymer or randomcopolymer, and poly(hydroxyalkanoate) and the at least first and secondmoieties are randomly or equally spaced from one another.
 4. Theelastomer material of claim 1, wherein the first moieties include4,4′-methylenebis(phenyl urea) (MPU) and the second moieties includeisophorone bisurea (IU).
 5. The elastomer material of claim 4, whereinthe particular ratio of MPU moieties to IU moieties is selected from thegroup consisting of: 0.4 to 0.6, 0.3 to 0.7 and 0.2 to 0.8.
 6. Theelastomer material of claim 1, wherein the elastomer material isconfigured and arranged to stretch up to 3,000 percent and exhibits aYoung's modulus of between 0.22 and 1.5 megapascal (MPa).
 7. Theelastomer material of claim 1, wherein the first moieties are configuredand arranged to form up to four dynamic bonds with another of the firstmoieties and the second moieties are configured and arranged to formless than four dynamic bonds with another of the second moieties.
 8. Theelastomer material of claim 1, wherein the elastomer material includes asupramolecular network formed as a polymer film configured and arrangedto exhibit the autonomous self-healing and notch-insensitive stretchingof 1,200-1,500 percent by self-recoverable energy dissipation in thepolymer film.
 9. An apparatus comprising: a polymer film that includes asupramolecular network of elastomer material, the elastomer materialhaving a flexible polymer backbone with a particular ratio of at leastfirst moieties and second moieties, the first moieties being configuredand arranged to provide a first number of dynamic bonds resulting frominteractions between the first moieties and the second moieties beingconfigured and arranged to provide a second number of dynamic bondsresulting from interactions between the second moieties, the secondnumber of dynamic bonds having a weaker bonding strength than the firstnumber of dynamic bonds, and wherein the polymer film exhibitsautonomous self-healing, a Young's modulus of between 0.1 and 3.0megapascal (MPa), and stretching of between 1,200 and 3,000 percentwithout rupturing.
 10. The apparatus of claim 9, wherein the polymerfilm is colorless and transparent, and the first moieties include4,4′-methylenebis(phenyl urea) (MPU) and the second moieties includeisophorone bisurea (IU), and the flexible polymer backbone is selectedfrom the group consisting of: polydimethylsiloxane (PDMS)polyethyleneoxide (PEO), Perfluoropolyether (PFPE), polybutylene (PB),poly(ethylene-co-1-butylene), poly(butadiene), hydrogenatedpoly(butadiene), polybutylene, poly(ethylene oxide)-poly(propyleneoxide) block copolymer or random copolymer, and poly(hydroxyalkanoate).11. The apparatus of claim 9, wherein the polymer film is configured andarranged to be stretched up to 3,000 percent and exhibits a Young'smodulus of between 0.22 and 1.5 MPa.
 12. The apparatus of claim 9,wherein the polymer film exhibits mechanical properties including theautonomous self-healing, the Young's modulus and the stretching due todifferent crosslink strength of the first and second numbers of dynamicbonds.
 13. The apparatus of claim 9, wherein the polymer film exhibitsnotch-insensitive stretching and a fracture energy of around 15,000Joule per meter squared (J/m2).
 14. The apparatus of claim 9, whereinthe polymer film is configured and arranged to exhibit the autonomousself-healing in a presence of liquid.
 15. The apparatus of claim 9,wherein the polymer film forms part of one of the following:three-dimensional self-healable objects, wearable electronics, roboticapplications, self-healable electrode, self-healable capacitive strainsensor, and an array of strain sensors.
 16. A method comprising:selecting a ratio of at least a first moiety and a second moiety basedon one or more designated mechanical properties; forming a viscoussolution that includes a flexible polymer and the ratio of the at leastfirst moiety and the second moiety; and from the viscous solution,forming a polymer film includes a supramolecular network of elastomermaterial, the elastomer material having a flexible polymer backbone thatincludes the flexible polymer with the selected ratio of the at leastfirst moieties and second moieties, the first moieties being configuredand arranged to provide a first number of dynamic bonds resulting frominteractions between the first moieties and the second moieties beingconfigured and arranged to provide a second number of dynamic bondsresulting from interactions between the second moieties, the secondnumber of dynamic bonds having a weaker bonding strength than the firstnumber of dynamic bonds, wherein the formed polymer film exhibitsautonomous self-healing, a Young's modulus of between 0.1 and 3.0megapascal (MPa), and stretching of at least 1,200 and 3,000 percentwithout rupturing.
 17. The method of claim 16, wherein selecting theratio of the at least first moieties and second moieties in the polymerfilm sets mechanical properties of the polymer film, wherein a decreasein the first moiety increases a fracture strain and decreases theYoung's modulus and fracture energy.
 18. The method of claim 16, whereinselecting the ratio of at least first moieties and second moieties inthe polymer film sets mechanical properties of the polymer film, whereinan increase in the first moiety increases the Young's modulus andfracture energy of the polymer film.
 19. The method of claim 16, whereinthe first moieties include 4,4′-methylenebis(phenyl urea) (MPU) and thesecond moieties include isophorone bisurea (IU), and the flexiblepolymer backbone is selected from the group consisting of:polydimethylsiloxane (PDMS) polyethyleneoxide (PEO), Perfluoropolyether(PFPE), polybutylene (PB), poly(ethylene-co-1-butylene),poly(butadiene), hydrogenated poly(butadiene), polybutylene,poly(ethylene oxide)-poly(propylene oxide) block copolymer or randomcopolymer, and poly(hydroxyalkanoate).
 20. The method of claim 16,wherein the polymer film is severed and the method further includeshealing the severed polymer film in water, wherein the healed polymerfilm is configured and arranged to stretch up to 1,100 percent withoutrupturing.